The present invention relates to improvements in apparatus for manipulating stacks of paper sheets and the like, and more particularly to improvements in apparatus for manipulating piles of superimposed stacks of sheets wherein neighboring stacks are separated from each other by panels of paperboard, cardboard, plastic material or the like. Still more particularly, the invention relates to improvements in apparatus for transferring successive stacks of a pile of superimposed stacks into a machine or apparatus wherein the stacks are converted into writing pads, steno pads, exercise books or other types of stationery products.
It is customary to assemble large sheets of paper or the like into stacks which are superimposed upon each other to form piles wherein each stack rests on a relatively stiff or reasonably still panel of paperboard or the like. The thickness or height of a discrete stack cannot exceed a maximum thickness which is still acceptable for further processing of the stack in a machine for making note books, steno pads, exercise books and like stationery products. In heretofore known production lines for pads or the like, such large stacks are lifted off a pile of superimposed stacks by hand and are introduced into a production line wherein successive stacks are automatically transported, severed and otherwise treated to convert them into pads or other types of stationery products. The stacks are delivered to the feeding station for individual stacks in the form of piles of superimposed stacks, and each stack rests on a discrete panel which is normally converted into the rear covers or backs of several pads, i.e., into the rear covers of those pads which are obtained by subdividing the respective stack into a plurality of smaller stacks and by bonding, wiring, stapling, sewing or otherwise securing the sheets of each smaller stack to each other.
The locus of feeding of discrete stacks of large sheets into an automatic production line constitutes a bottleneck because it is not always possible to manually feed successive stacks at the required rate. A serious problem is that of rapidly separating the topmost stack and the panel beneath the topmost stack from the next-to-the-topmost stack of a pile of superimposed stacks.
British Pat. No. 2 090 815 discloses a method according to which the panels between successive stacks of a pile of such stacks are offset relative to the neighboring sheets so that a portion of each panel projects from the pile. The method comprises the step of applying suction to the projecting portion of the topmost panel in the pile so that the panel is lifted and defines with the sheet immediately below it a gap which can receive a sword-like separating element serving to further separate the topmost stack and the panel below it from the remainder of the pile. A drawback of such proposal is that the projecting portions of the panels are wasted as well as that it is not always possible to readily lift the panels and the stacks thereabove by suction.
German Offenlegungsschrift No. 27 53 301 proposes to ascertain the number of sheets to be lifted off a pile, either by selecting the level of a separating finger which is to penetrate into the edge face of a pile or by actually counting the number of sheets from the topmost sheet down. Once a selected number of sheets has been counted, the separating finger is caused to penetrate beneath the last-counted sheet and provides a gap between the thus obtained topmost stack and the stack therebelow. This is a time-consuming and cumbersome procedure.